The Nervous System

The Nervous System

  • A stimulus is a change in the environment that you may need to react to.
  • We have five sense organs: eyes, ears, nose, tongue and skin. They all contain different receptors which are groups of cells sensitive to a stimulus.
  • They change stimulus energy to an electrical impulse.
  • A stimulus can be light, sound, taste, temperature etc.
  • Path of a neurone response:
    • stimulus (change in environment) à receptor (cells that detect the change) à sensory neurone à relay neurone à motor neurone à effector muscle à response

The response

  • When a stimulus is detected, the information is sent in the form of electrical impulses along the sensory neurones to the central nervous system (CNS).
  • The CNS is the brain and the spinal cord.
  • CNS coordinates the response.
  • The CNS then sends information to an effector along a motor neurone. The effector responds accordingly.


  • Muscles and glands are the effectors and they respond in different ways.
  • Muscles contract in response to a nervous impulse whereas glands secrete substances as a response.


Sensory neurones

  • Long Dendrons and short axons carry nerve impulses from the receptors in the sense organs to the CNS.

Motor Neurones

  • Many short dendrons and one long axon to carry nerve impulses from the CNS to the effectors.

Relay Neurones

  • Many short dendrons and axons carry nerve impulses from sensory neurones to motor neurones.